Landon Conner's father, Chris, was going for a neighborhood stroll a few years ago when suddenly he collapsed. His heart had stopped beating, and though the ambulance was there in minutes, it was too late to revive the 39-year-old man with defibrillator paddles.

So last month Landon, 13, who was born with the same heart abnormality as his father, got his own personal "paddle" implanted under the skin of his left armpit.

This palm-size defibrillator has been available for adults for several years, and now Children's Hospital of Philadelphia is among a handful of facilities that specialize in putting the device in children.

Landon underwent his procedure Jan. 25, and all seemed to go smoothly.

But before CHOP cardiologist Maully Shah could pronounce her handiwork a success, she needed to take a dramatic step: Stop the teenager's heart to see if his new device, made by Boston Scientific of Marlborough, Mass., would start it again.

"We're going to induce a cardiac event," Shah announced to the operating-room team at 10:33 a.m. "Everybody ready?"

Beep, beep, beep . . . went the monitor measuring the boy's heart rate.

Until Shah gave the signal to deliver a swift electric current to the patient's heart, and abruptly, the beeping stopped.

Hypertrophic cardiomyopathy affects 1 in 500 people, according to the American Heart Association, usually characterized by an abnormally thick wall of the left ventricle.

Shah said the heart muscle cells are arranged "in a chaotic manner," which can lead to impaired blood flow and scarring.

Some people have no symptoms. Others may experience shortness of breath or abnormal rhythms. On rare occasions, typically during strenuous physical activity, a person with the condition will experience sudden cardiac arrest.

Perhaps the best-known case came in 1990, when hypertrophic cardiomyopathy was blamed in the death of Loyola Marymount University basketball star Hank Gathers, a high school star at Dobbins Tech. Last year, the Philadelphia Medical Examiner's Office said the condition caused the death of Ryan Gillyard, a freshman at St. Joseph's Preparatory School who collapsed during spring football conditioning.

Then there was Chris Conner in 2011, who was merely going for a walk with his wife, Amy.

'Kind of scary'

At the advice of a pediatrician, Landon and his older brother, Logan, were tested to see if they, too, had the condition. Both did, and were deemed to have an elevated risk of sudden cardiac death.

Landon was playing in a youth soccer league at the time.

"It was kind of scary just to watch him run," his mother said.

Both boys, who live with their mother in McConnellsburg, Pa., southwest of Harrisburg, got defibrillator implants at CHOP.

Logan, now 15, went first, three years ago, with an older type of device that goes inside the chest wall beneath the collarbone. The electrode from that device is inserted through a vein into the heart.

It works, but in younger people who are active and still growing, the electrode wires have been known to break, requiring repeat surgery. Some manufacturers tried to make the wires stronger, but those were prone to perforating the heart, Shah said.

'A mule kick'

By the time Landon was ready for surgery this year, Shah had the option of Boston Scientific's less invasive Emblem device, which is placed beneath the skin.

Its electrode wire is much stronger, said Shah, the hospital's director of cardiac electrophysiology, as she prepared for Landon's surgery.

"If you hang on there, I think you'd be OK," the physician said, giving the wire a vigorous tug. "I think it's really a godsend for children."

Though its electrode does not directly touch the heart like the wires on previous implants, the under-the-skin device is nevertheless able to deliver a wallop.

If its internal software senses a dangerous arrhythmia or an abnormally fast heartbeat - both of which can mean imminent cardiac arrest - the device jolts the heart with 80 joules of energy.

"The most common description is that it's like a mule kicking you in the chest," Shah said.

The physician proceeded to cut a pocket in the skin under her patient's left arm. She made additional incisions in his chest, so she could insert the device's electrode wire across the area above his heart.

It was time for the big test. The electric current sent Landon's heart into ventricular fibrillation, and the room went quiet. His heart was still quivering weakly and rapidly, but its normal pumping action had stopped.

Joseph Brozoski, a representative from the device-maker who was present for the surgery, checked a computer readout of the implant's activity.

"It's sensing appropriately," he announced.

Then came the mule kick. The patient was under anesthesia and did not move in response. But sure enough, 14 seconds after his heart had stopped, it started again. Beep, beep, beep . . .

If the device had not worked, physicians and nurses had traditional paddles at the ready, along with medication. And if that hadn't worked, they could still use extracorporeal membrane oxygenation, a form of life support.

But all was fine. The eighth grader spent the night in the hospital, followed by another night in a hotel, and then it was back to school.

Studies have found the device resuscitates patients well over 95 percent of the time. The main drawback is that on occasion, it will incorrectly sense a problem and deliver an unnecessary shock. Its battery lasts seven years on average, after which patients must come back to the hospital for a replacement.

On average, Medicare reimburses hospitals about $31,000 for the procedure in adults if done on an outpatient basis, more for inpatients. Rates for Medicaid, which covers some child patients, vary by state. And not all patients are candidates for the device, depending on their heart rhythm.

Last week, Landon said he felt "pretty good."

He finds that he can't sleep on his left side because he feels the lump under his skin. And contact sports are out.

Overall, there is a sense of ease.

"It's different, because I feel a little bit safer," the teenager said.

Ditto, said his mother.

"It's nice to know that's there now if anything does happen," she said.

Shah, the physician, was pleased with her work but said the really difficult part fell to the patient's mother.

"I have to tell her I'm going to induce cardiac arrest," Shah said. "Basically, I'm telling her, 'Your child's going to die on the table, and I'm going to resuscitate him.' And she sits through this."

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@TomAvril1